The present invention relates to a scanning probe nanolithography system and a control method of scanning probe nanolithography processes.
Scanning probe nanolithography systems are known from a plurality of prior art documents, e.g. U.S. Pat. No. 8,261,662, reciting further publications.
Nanolithography is usually done in an open-loop way, meaning that all writing/patterning parameters have to be set prior to the writing/patterning process. No information from the written nanostructure is obtained during the writing process. Therefore, all external (temperature, humidity, pressure, . . . ) or internal (thermal drift, noise, fluctuations, degradations, ageing . . . ) influences, that potentially disturb the writing/patterning process have to be shielded, eliminated or accounted for during the writing process in order to obtain nanostructures of high quality and good reproducibility.
Feedback loops as mentioned in U.S. Pat. No. 8,261,662 are used to control system writing parameters of the writing process, e.g. control of writing current through measurements of said current.
Scanning Probe Lithography techniques use sharp tips/probes to create nanostructures. This can be done, for example, by mechanical interactions (nano-shaving or nanoscratching as e.g. described by Yan et al., Small, 6(6):724-728, (2010)), with electrical fields between the tip and the sample (local anodic oxidation, see e.g. Chen et al., Optics letters, 30(6):652-654, (2005), field-induced deposition, see e.g. Rolandi et al. Angewandte Chemie International Edition, 46(39):7477-7480, (2007), field emission of electrons), light enhancement at the tip (near-field lithography, see e.g. Srituravanich et al., Nature Nanotechnology, 3.12 733-737, (2008)), deposition of material from the tip (dip pen lithography, see e.g. Radha et al., ACS nano, 7.3:2602-2609, (2013)) or local heating of the tip (thermochemical, thermal desorption lithography, see e.g. Pires et al., Science, 328, 732, (2010)). Usually, scanning probe lithography methods scan the surface line by line and write the nanostructures pixel by pixel along the lines.
The specification incorporates by reference the disclosure PCT/EP2014/069667.
The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.
In many cases, the same tip that creates the nanostructures can be used to image/read (like an Atomic Force Microscope (AFM) or a Scanning Tunneling Microscope (STM)) the nanostructures also in a line by line and pixel by pixel manner. The information/property to image/read the surface with the nanostructures is most of the time topography, but can also be e.g. friction, thermal conductivity, electrical conductivity, electrostatic potential, magnetic moment, adhesion, elastic modulus or further surface properties that can be measured by standard scanning probes microscopy techniques.
US201126882A1 is an example how external parameters (in this case leveling of the substrate) need to be measured and adjusted prior to the patterning of nanostructures.
In contrast to prior art US201126882A1, the present invention starts with the patterning process and takes the information from deviations of the target nanostructure to adjust the external parameters. This closed-loop lithography concept could potentially be applied also to solve the problem described in patent US201126882A1, which is the leveling of multiple cantilevers, in a more elegant and faster way.
U.S. Pat. No. 7,060,977B1 describes a typical calibration process that is used for many scanning probe nanolithography processes. First a “nanoscale test pattern” is fabricated. The test pattern is measured afterwards by some other means to deduct the relevant calibration parameters for the real patterning. The method allows doing the calibration and the actual application “on the same day”.
The present invention does the measurement of the nanostructures continuously and during the lithography process for each line and hence within typically 10 ms to 100 ms.
U.S. Pat. No. 5,825,670A describes a method how the information from imaging of a calibration sample using scanning probe microscope can be used to reduce errors due to non-linearity in the scanner motion. It is mentioned that this calibration can also be used to better control the positioning for scanning probe lithography, where a precise positioning is even more important than for imaging.
The present invention images during the lithography process. The information of each imaged line can also be used to detect deviations from the xy position, e.g. through thermal drift, and correct for them.
Scanning probe microscopy has been combined with scribing methods like in U.S. Pat. No. 5,327,625A. Here, a scribing tool indents nanostructures into a surface and a separate scanning probe microscope is used to measure the indentations.
In the present invention the same probe is used for writing and imaging.
In Scanning Tunneling Microscopy (STM) the imaging speed depends a lot on the feed-back loop of the imaging process. Previous imaged lines can be used to predict the topography of the next imaged line and can hence help to make the feed-back loop faster, as is described in U.S. Pat. No. 4,889,988 A.
The present invention uses the fact that for each line the imaging information meaning the property of the nanostructure, like the topography in thermal scanning probe lithography, is already roughly known before the actual imaging process because the target property of the nanostructure of the writing process is known at the respective line. Hence, the imaging parameters can be optimized for speed and nondestructive imaging. This can mean for example in the case of topography that the z-positioning moves according to the target writing topography so that the probe is still in contact to measure the actual topography but without strong potentially destructive forces because the cantilever exerts a weaker force on the surface.